A subdomain is the part of the web address that's before a domain and you have quite possibly seen a lot of subdomains while surfing around the Web. As an illustration, many sites such as Wikipedia have versions in different languages using subdomains - en.wikipedia.org, de.wikipedia.org and so forth. The main benefit of employing a subdomain is that it can have an independent website and its own records, so you are able to even host it on a different server. The practical use is that you can have a supplementary site, such as an e-learning portal for college students in addition to the primary school website. If you use subdomains rather than subfolders, it'll be much easier to perform maintenance or to upgrade a certain website, not mentioning that it's going to be more safe to have the sites separate from one another.